Kit for the determination of L-carnitine in biological fluids and tissues

ABSTRACT

A kit for the determination of L-carnitine or short-chain acyl L-carnitines consisting of only two vials complete with all the necessary reactants, with the exception of standards, preferably the kit contains the reactants in lyophilized form.

This application is the US national phase of international application PCT/IT01/00166 filed 30 Mar. 2001 which designated the U.S.

The invention described herein relates to a kit for the determination of L-carnitine in biological fluids.

BACKGROUND TO THE INVENTION

L-carnitine plays a fundamental role in metabolism, being a key element in the oxidation of long-chain fatty acids and thus in the production of energy.

There are many pathological states the underlying cause of which is a deficiency of L-carnitine, and L-carnitine determination is necessary in order to establish the precise a etiology of the related disease processes.

There has been a growing awareness among clinicians over recent years of the importance of L-carnitine deficiencies (Bieber et is al. Fed. Proc. 41, 2858 (1982); Stanley, Adv. Pediatr. 34, 59 (1987).

One of the first methods used for determining L-carnitine (hereinafter called carnitine for short) was described by Marquis and Fritz in 1964 (Journal of Lipid Research 5, 184-187). Various other methods have been described, such as, for example, those by Marzo et al., J. Chromatogr. 527, 247 (1990); and Hoppel, in: Hommes (ed.), Techniques in Diagnostic Human Biochemical Genetics, New York, Wiley-Liss, 309-326 (1991).

The most widespread methods are based on the reaction of the enzyme carnitine acetyl transferase (CAT; EC 2.3.1.7):

One very widespread method for the indirect determination of carnitine is based on the reaction of acetyl-Coenzyme A, released by the preceding reaction with 5,5′-dithiobis-2-nitrobenzoate (DTNB), which in turn releases the thiophenylate ion, which is determined spectrophotometrically at 412 nm (see, in addition to the above-mentioned Marquis, Seccombe D. W., Clinical Chemistry, 22, No. 10, 1589-1592, 1976; Pearson, Methods of Enzymatic Analysis, 4, 1758-1771, 2nd edition—Bergmeyer; Casillas E. R. Biochimica et Biophysica Acta, 184, 566-577, 1969; Cederblad G. Clinica Chimica Acta, 33, 117.123, 1971; Carrier H. N., Muscle & Nerve July/August 326-328, 1980). This method determines free carnitine. For the determination of the short-chain acyl carnitines, and thus of total carnitines, the sample is subjected to alkaline hydrolysis, converting the acyl carnitines to free carnitine.

The known methods entail elaborate preparation phases, or use techniques which are only poorly conducive to automation of the analyses. For a discussion of the subject, see U.S. Pat. No. 5,316,917, filed in the name of Duke University, and incorporated herein for reference purposes. This patent aims to solve the problem of the automation of the analyses. This need is strongly felt in clinical laboratories that have to carry out large numbers of determinations. The Duke University patent offers the solution of an automated spectrophotometric method, consisting in the following steps:

-   1) addition of a plurality of samples of deproteinized biological     fluids to a set of wells of a centrifugal spectrophotometric     analyzer; -   2) addition to each sample of:     -   a) acetyl-Coenzyme A in an amount sufficient to react         essentially with all the free carnitine in the sample to produce         acetyl-carnitine and free Coenzyme A;     -   b) DTNB in an amount sufficient to convert essentially all the         Coenzyme A produced in the previous reaction to thiophenylate,         and then     -   c) simultaneously combine CAT, in each sample, in an amount         sufficient to set off the reaction between acetyl-Coenzyme A and         free carnitine and bring it to completion, and then     -   d) determine the amount of thiophenylate present in the sample         simultaneously by spectrophotometry.     -   The kit used to implement the method described in the patent         cited includes:         -   a) a first container containing a solution of DTNB at a             concentration ranging from 0.27 to 27 mmol/L, at a pH             ranging from 6.5 to 8.5, and         -   b) a second container containing a solution consisting of             acetyl-Coenzyme A at a concentration ranging from 1.2 to 120             mmol/L, where the two solutions can be mixed together prior             to use to form a solution containing DTNB at a concentration             ranging from 0.23 to 23 mmol/L and acetyl-Coenzyme A at a             concentration ranging from 0.17 to 17 mmol/l.

In actual fact, the kit must also include a third container containing from 4 to 40 kU/L of CAT, for example in the form of a solution at a concentration ranging from 1.72 to 172 kU/L. It is envisaged that the third container should contain CAT in lyophilized form. Also envisaged in the kit are containers with carnitine standards in aqueous solution from 0.1 to 10 mmol/L and of octanoyl L-carnitine from 0.1 to 10 mmol/L. Also provided in the kit is a fourth container containing a 3-[N-morpholine]propanesulphonic acid hydrochloric solution, from 0.1 to 10 mmol/L.

The execution of the procedure entails the preparation of 4 solutions:

-   -   1. DTNB; HEPES; EDTA at pH 7.5     -   2. MOPS-HCl     -   3. KOH

In fact, the procedure described in the patent is called “three reagent chemistry”.

It is known that the solutions envisaged in the kit described above must be stored at low temperature, from 0 to 4° C., as prescribed in the patent cited.

U.S. Pat. No. 6,027,690, a divisional patent of U.S. Pat. No. 5,872,008, filed in the name of Bair and Shug, provides a kit for the diagnosis of premenstrual syndrome, based on the determination of free and total carnitine in the blood. Apart from the specific indication of the method, to implement the method the kit consists of:

-   -   a) a first container containing a solution of acetyl-Coenzyme A         at a concentration ranging from 1.2 to 120 mmol/L, and     -   b) a second container containing a solution consisting of DTNB         or N-(p-2(benzimidazolyl)phenyl)maleimide at a concentration         ranging from 0.27 to 27 mmol/L at a pH ranging from 6.5 to 8.5,         where the two solutions can be mixed together prior to use to         form a solution consisting of DTNB or         N-(p-2(benzimidazolyl)phenyl)maleimide at a concentration         ranging from 0.23 to 23 mmol/L and acetyl-Coenzyme A at a         concentration ranging from 0.17 to 17 mmol/l.

In the execution of the procedure according to U.S. Pat. No. 6,072,690, the method described in U.S. Pat. No. 5,316,917 can be adopted amongst others.

A Boehringer Mannheim kit is commercially available for the determination of L-carnitine in plasma, seminal fluid, and urine. The determination is based on the following reactions:

The amount of NADH consumed during the reaction is equivalent to half the amount of L-carnitine. NADH is determined by absorbance at 334 (Hg), 340 or 365 (Hg) nm.

The kit comprises:

-   -   1) 3 vials (1) each containing 0.7 g of a Coenzyme/buffer         mixture consisting of Tris buffer pH 7.0, NADH 5 mg, ATP 6 mg,         acetyl-Coenzyme A 4 mg, PEP 3 mg, magnesium acetate, and         stabilizing agents.     -   2) Vial (2) containing approximately 3 ml of enzyme suspension         consisting of acetyl-CoA synthetase (ACS), 2U approx., myokinase         (MK), 160 U approx., lactate dehydrogenase (LDH), 240 U approx.,         and pyruvate kinase (PK), 240 U approx.     -   3) Vial (3) containing 0.2 ml of carnitine acetyl transferase         (CAT) enzyme suspension, 60 U approx.     -   4) Vial (4) containing L-carnitine standard.     -   5) Vial (5) containing detergent solution.

Prior to use, the contents of one vial (1) are diluted with 10 ml of distilled water and 1 ml is added from vial (5). The other vials are used as such. The procedure consists in the addition of the sample (or standard) to solution (1), then addition of suspension (2), measurement of absorbance, then addition of suspension (3) and subsequent measurement of absorbance.

BRIEF SUMMARY OF THE INVENTION

It has now been found that it is possible to provide a kit for the determination of L-carnitine or short-chain acyl L-carnitines consisting of only two vials complete with all the necessary reactants, with the exception of the standards. Conveniently, the kits contain the reactants in lyophilized form.

One of the advantages afforded by the realization of the invention described herein consists in the possibility of determining carnitine over a broad range of concentrations.

The kit according to the invention comprises:

-   -   a) a first container containing Reagent 1, said Reagent 1         consisting of HEPES, EDTA, acetyl-Coenzyme A and DTNB;     -   b) a second container containing Reagent 2, said Reagent 2         consisting of carnitine acetyl transferase.

Therefore, one subject of the invention described herein is a kit for the determination of L-carnitine in biological tissues and fluids, its use for the determination of L-carnitine in biological tissues and fluids and methods for the determination of L-carnitine in biological tissues and fluids using the kit.

According to the invention described herein, the kit permits the determination of L-carnitine in biological fluids and tissues. Examples of biological fluids and tissues are blood, plasma and seminal fluid. When suitably treated according to conventional techniques, other tissues can be analyzed with the kit according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In a first preferred form, Reagent 1 consists of:

HEPES 0.1 M, pH 7.5 EDTA 50 mM, pH 7 acetyl-Coenzyme A DTNB 10, 1 mM

Preferably, Reagent 1 has the following composition per ml:

HEPES 0.1 M, pH 75 0.652 mL EDTA 50 mM, pH 7 0.174 mL acetyl-Coenzyme A 0.087 mL DTNB 10.1 mM 0.087 mL

The Reagent 1 container preferably contains 3 mL of Reagent 1.

In a first preferred form, Reagent 2 consists of:

-   -   carnitine acetyl transferase 0.500 mL

If deemed appropriate, the kit may also contain other elements such as L-carnitine standards, other reactants for the preparation of samples, e.g. plasma or seminal fluid. Reagents 1 and 2 may also essentially contain, in addition to the basic reactants necessary for the reactions, i.e. acetyl-Coenzyme A, DTNB and carnitine acetyl transferase, additional substances useful for the analysis, or alternative substances to those contained in the kit capable of producing the same effect, e.g. buffers, chelating agents, complexing agents, pH correctors, preservatives, and stabilizing agents. Any changes or improvements to the kit supplied on the basis of the invention described herein, which substantially lead to the same result and afford the same advantages fall within the compass of the invention described herein.

The preferred form of the kit is that in which the reagents are in lyophilized form. This form permits prolonged storage of the reagents in normal ambient conditions, without particular precautions, with obvious advantages from the point of view of the marketing of the kit. The lyophilization is done according to the conventional techniques used in the field and requires no further description.

The kit according to a first embodiment of the invention described herein (3 mL of Reagent 1 and 0.500 mL of Reagent 2) is sufficient for approximately 13 determinations, if the manual method is used, or for approximately 60 determinations, if the automatic method is used. Both methods are described in detail here below.

A first preferred embodiment of the invention described herein relates to the determination of carnitine in plasma.

The invention described herein is based on the reaction that takes place between L-carnitine and acetyl-CoA in the presence of the enzyme carnitine acetyl transferase (CAT). The Coenzyme A (CoA) produced by this reaction reacts in turn with 5.5°-dithiobis-2-nitrobenzoate (DTNB), releasing thiophenylate ions (TNB−) which absorb at a wavelength of 412 nm, in the case of the use of a manual spectrophotometer, or at a wavelength of 405 nm, in the case of the use of an automatic-type spectrophotometer. The reactions involved are all quantitative, and therefore the TNB− absorbance value can be used to determine the carnitine concentration in the sample.

The invention is illustrated with reference to a preferred form of its embodiment, namely for the determination of carnitine in plasma. It is understood that the principles involved in the invention described herein are equally applicable to other tissues, which are treated according to their nature, using conventional procedures which are a matter of general knowledge to people with average experience in the field. The determination method comprises the following steps:

a) deproteinizing of the plasma sample in an acid milieu;

b) neutralization of the sample;

c) incubation.

It is in step c) that the enzymatic reactions occur using the kit according to the invention described herein:

The amount of TNB− ions forming in the latter reaction is equivalent to that of the L-carnitine initially present in the sample.

Ambient pH weakly influences the reactions and therefore the result of the analysis; in fact, at pH above 8.5 CAT is inactivated, whereas at pH values below 7 the dissociation of DTNB is incomplete, and therefore the L-carnitine values will be underestimated.

As an alternative to steps a) and b) described above, the sample can be deproteinized by simple filtration.

EXAMPLE 1 Preparation of Solutions

Acetyl-CoA 12.35 mM: solubilize 86 mg of acetyl-CoA in 8.6 mL of bidistilled water. This solution will be used to prepare Reagent 1.

Carnitine acetyl-transferase (CAT): dilute the CAT with bidistilled water (1 volume of CAT+11 volumes of bidistilled water). This solution will be used to prepare Reagent 2. If not used immediately, the reagent can be stored at −20° C. and defrosted at the time of use.

EDTA 50 mM pH 7.0: solubilize 2.2 g of EDTA in 50 mL of bidistilled water in a 100 mL calibrated flask. Bring the pH to 7.0 with glacial acetic acid and top up to volume with bidistilled water. The solution is stable for 6 months at 4° C.

DTNB 10 mM: solubilize 34.4 mg of DTNB with 8.6 ml of Hepes 0.1 M at pH 7.5.

Hepes 0.1 M at pH 7.5: solubilize 2.38 g of Hepes in 50 mL of bidistilled water in a 100 mL calibrated flask. Bring the pH to 7.5 with potash 1.25 M, and top up to volume with bidistilled water. The solution is stable for 6 months at 4° C.

Perchloric acid 2.75 M: dilute 23.2 mL of 70% perchloric acid in bidistilled water in a 100 mL calibrated flask. The solution is stable for 6 months at ambient temperature.

Potassium carbonate 1.2 M: solubilize 16.6 g of potassium carbonate with 80 mL of bidistilled water. Mix and top up to volume with bidistilled water. The solution is stable for 6 months at ambient temperature.

Potassium hydroxide 1.25 M: solubilize 8.25 g of potassium hydroxide with 80 mL of bidistilled water a 100 mL calibrated flask. Mix and top up to volume with bidistilled water. The solution is stable for 6 months at ambient temperature.

Reagent 1: prepare 100 mL of reagent: to 65.5 mL of Hepes 0.1 M at pH 7.5 add 17.3 mL of EDTA 50 mM, pH 7.0, 8.6 mL of DTNB 10 mM and 8.6 mL of acetyl-CoA 12.35 mM. The solution is stable for 6 months at −20° C.

Deproteinizing of Plasma/Serum and Neutralization of Sample

Transfer 300 μL of plasma/serum and 40 μL of perchloric acid 2.75 M into a 1.5 ml Eppendorf tube. Mix well and then centrifuge at 10,000×g for 5 min at 4° C. Transfer 250 μL of the supernatant and add 40 μL of potassium carbonate 1.2 M in a 1.5 ml Eppendorf tube. Mix and then leave the samples to digest in ice for 10 min. Centrifuge again at 10,000×g for 5 min at 4° C. Remove the supernatant for analysis.

Deproteinizing of Plasma/Serum by Filtration

Load the sample of plasma/serum on AMICON type filters with cut-off ranging from 5000 to 20000 NMW. Load the sample (400 μL approx.) in an Eppendorf tube containing the filter, to be centrifuged at 15000×g for 30-40 minutes at 4° C. Remove the filtrate for analysis.

Enzymatic Analysis

A) Manual type spectrophotometry.

Varian DMS-80 UV/VIS spectrophotometer

Wavelength: 412 nm

Cuvette: single-use, disposable, 1 cm optical path

Temperature: 20-25° C.

Measurement: against air.

Incubation:

transfer to cuvette

Blank (μL) Sample (μL) Bidistilled water 1000 750 Sample — 250 Reagent 1  230 230

Stir. After 5 minutes measure the absorbance of the blank and the sample (A₁). On completion of reading, add 20 μL of CAT (Reagent 2) to each test tube and mix. After another 10 minutes repeat the measurement of the blank and the sample (A₂).

The concentration is calculated as follows: $C = {\frac{\Delta\quad A}{ɛ \times d} \times F \times 1000}$

-   -   where:     -   C=concentration of sample (nmol/mL)     -   ΔA=(A₂−A₁)_(sample)−(A₂−A₁)_(blank)     -   ε=coefficient of molar extinction of TNB−         (412 nm=13.6 L×μmol⁻¹×cm)     -   d=optical path length (cm)     -   F=dilution factor (6.55)     -   1000=conversion factor to obtain the result in nmol/mL.

Example of calculation:

A₁ A₂ A₂-A₁ Blank 0.169 0.172 0.003 Sample 0.170 0.242 0.072

Applying the formula indicated above: C=33.2 nmol/mL.

B) Automatic Type Spectrophotometer

Before starting the analysis, dilute Reagent 1 and Reagent 2 5 times with bidistilled water (e.g., to 1 mL of Reagent 1 add 4 mL of bidistilled water; to 1 mL of Reagent 2 add 4 mL of bidistilled water).

Experimental Conditions

Procedure for programming the Roche mod. Cobas-Mira S automatic analyzer (software used N* 8347)

FREE CARNITINE SW 884*7 COBAS MIRA S GENERAL MEASUREMENT MODE ABSORB REACTION MODE D-R-S-SRI CALIBRATION MODE LIN REGR REAGENT BLANK REAG/SOL CLEANER NO WAVELENGTH 405 nm DECIMAL POSITION  2 UNIT μmol/L ANALYSIS DILUTION NAME H₂O FACTOR NO TIME NO STD: MAIN DIRECT MAIN STD 200 μmol/L POST DIL FACTOR  3 CONC. FACTOR NO SAMPLE CYCLE  1 VOLUME  50 μL DILUTION NAME H₂O VOLUME  10 μL REAGENT CYCLE  1 VOLUME 250 μL START R1 CYCLE  7 VOLUME  40 μL DILUTION NAME H₂O VOLUME  10 μL CALCULATION SAMPLE LIMIT  0.1 POINT T1 REAC. DIRECTION INCREASE CHECK ON CONVERS. FACTOR  1 OFFSET  0 TEST RANGE LOW ON HIGH ON NORMAL RANGE LOW YES HIGH NO NUMBERS OF STEPS  1 CALC. STEP A ENDPOINT FIRST READING  6 LAST READING 30 CALIBRATION CALIB. INTERVAL ON REQUEST BLANK REAGENT RANGE LOW −0.0001 HIGH  0.1000 BLANK RANGE LOW −0.0050 HIGH  0.0050 STANDARD POS:  1 1: 200 μmol/L 2: 100 μmol/L 3:  75 μmol/L 4:  50 μmol/L 5:  30 μmol/L 6:  20 μmol/L 7:  10 μmol/L 8:  0 μmol/L REPLICATE DUPLICATE DEVIATION 10% CORRECTION STD NO CONTROL CS1* POS: 11 LOW 90 mol/L ASSIGN 100 μmol/L HIGH 110 μmol/L CS2* POS: 12 LOW 40 μmol/L ASSIGN 50 μmol/L HIGH 60 μmol/L CS3* POS: 13 LOW 12 μmol/L ASSIGN 20 μmol/L HIGH 28 μmol/L

Note: the samples called CS1, CS2 e CS3 refer to the reference standards and are prepared by scalar dilution of the mother solution of L-carnitine inner salt at a concentration of 200 μmol/L.

The calculation of the concentrations of the blanks is done automatically by the analyzer which extrapolates them from a straight calibration line to be prepared fresh for each analysis session (possibly in duplicate).

The above-described sample preparation and analysis conditions being equal, it is possible to calculate the carnitine concentration for an unknown sample immediately by multiplying its absorbance value by the factor 1028.382. In this case neither the calibration line nor the control samples will be used.

Whenever the unknown samples have been deproteinized by acidification and subsequent neutralization with the procedure described above, the value of the concentration obtained must be multiplied by the factor 1.3146.

Given here below, by way of an example, is a table directly correlating the L-carnitine concentrations with the absorbance readings.

CALCULATION OF L-CARNITINE CONCENTRATIONS USING THE FACTOR 481.62 Abs μmoli/L Abs μmoli/L Abs μmoli/L Abs μmoli/L Abs μmoli/L Abs μmoli/L 0.001 0.482 0.051 24.563 0.101 48.644 0.151 72.725 0.201 96.806 0.251 120.89 0.002 0.963 0.052 25.044 0.102 49.125 0.152 73.206 0.202 97.287 0.252 121.37 0.003 1.445 0.053 25.526 0.103 49.607 0.153 73.688 0.203 97.769 0.253 121.85 0.004 1.926 0.054 26.007 0.104 50.088 0.154 74.169 0.204 98.250 0.254 122.33 0.005 2.408 0.055 26.489 0.105 50.570 0.155 74.651 0.205 98.732 0.255 122.81 0.006 2.890 0.056 26.971 0.106 51.052 0.156 75.133 0.206 99.214 0.256 123.29 0.007 3.371 0.057 27.452 0.107 51.533 0.157 75.614 0.207 99.695 0.257 123.78 0.008 3.853 0.058 27.934 0.108 52.015 0.158 76.096 0.208 100.18 0.258 124.26 0.009 4.335 0.059 28.416 0.109 52.497 0.159 76.578 0.209 100.66 0.259 124.74 0.010 4.816 0.060 28.897 0.110 52.978 0.160 77.059 0.210 101.14 0.260 125.22 0.011 5.298 0.061 29.379 0.111 53.460 0.161 77.541 0.211 101.62 0.261 125.70 0.012 5.779 0.062 29.860 0.112 53.941 0.162 78.022 0.212 102.10 0.262 126.18 0.013 6.261 0.063 30.342 0.113 54.423 0.163 78.504 0.213 102.59 0.263 126.67 0.014 6.743 0.064 30.824 0.114 54.905 0.164 78.986 0.214 103.07 0.264 127.15 0.015 7.224 0.065 31.305 0.115 55.386 0.165 79.467 0.215 103.55 0.265 127.63 0.016 7.706 0.066 31.787 0.116 55.868 0.166 79.949 0.216 104.03 0.266 128.11 0.017 8.188 0.067 32.269 0.117 56.350 0.167 80.431 0.217 104.51 0.267 128.59 0.018 8.669 0.068 32.750 0.118 56.831 0.168 80.912 0.218 104.99 0.268 129.07 0.019 9.151 0.069 33.232 0.119 57.313 0.169 81.394 0.219 105.47 0.269 129.56 0.020 9.632 0.070 33.713 0.120 57.794 0.170 81.875 0.220 105.96 0.270 130.04 0.021 10.114 0.071 34.195 0.121 58.276 0.171 82.357 0.221 106.44 0.271 130.52 0.022 10.596 0.072 34.677 0.122 58.758 0.172 82.839 0.222 106.92 0.272 131.00 0.023 11.077 0.073 35.158 0.123 59.239 0.173 83.320 0.223 107.40 0.273 131.48 0.024 11.559 0.074 35.640 0.124 59.721 0.174 83.802 0.224 107.88 0.274 131.96 0.025 12.041 0.075 36.122 0.125 60.203 0.175 84.254 0.225 108.36 0.275 132.45 0.026 12.522 0.076 36.603 0.126 60.684 0.176 84.765 0.226 108.85 0.276 132.93 0.027 13.004 0.077 37.085 0.127 61.166 0.177 85.247 0.227 109.33 0.277 133.41 0.028 13.485 0.078 37.566 0.128 61.647 0.178 85.728 0.228 109.81 0.278 133.89 0.029 13.967 0.079 38.048 0.129 62.129 0.179 86.210 0.229 110.29 0.279 134.37 0.030 14.449 0.080 38.530 0.130 62.611 0.180 86.692 0.230 110.77 0.280 134.85 0.031 14.930 0.081 39.011 0.131 63.092 0.181 87.173 0.231 111.25 0.281 135.34 0.032 15.412 0.082 39.493 0.132 63.574 0.182 87.655 0.232 111.74 0.282 135.82 0.033 15.893 0.083 39.974 0.133 64.055 0.183 88.136 0.233 112.22 0.283 136.30 0.034 16.375 0.084 40.456 0.134 64.537 0.184 88.618 0.234 112.70 0.284 136.78 0.035 16.857 0.085 40.938 0.135 65.019 0.185 89.100 0.235 113.18 0.285 137.26 0.036 17.338 0.086 41.419 0.136 65.500 0.186 89.581 0.236 113.66 0.286 137.74 0.037 17.820 0.087 41.901 0.137 65.982 0.187 90.063 0.237 114.14 0.287 138.22 0.038 18.302 0.088 42.383 0.138 66.464 0.188 90.545 0.238 114.63 0.288 138.71 0.039 18.783 0.089 42.864 0.139 66.945 0.189 91.026 0.239 115.11 0.289 139.19 0.040 19.265 0.090 43.346 0.140 67.427 0.190 91.508 0.240 115.59 0.290 139.67 0.041 19.746 0.091 43.827 0.141 67.908 0.191 91.989 0.241 116.07 0.291 140.15 0.042 20.228 0.092 44.309 0.142 68.390 0.192 92.471 0.242 116.55 0.292 140.63 0.043 20.710 0.093 44.791 0.143 68.872 0.193 92.953 0.243 117.03 0.293 141.11 0.044 21.191 0.094 45.272 0.144 69.353 0.194 93.434 0.244 117.52 0.294 141.60 0.045 21.673 0.095 45.754 0.145 69.835 0.195 93.916 0.245 118.00 0.295 142.08 0.046 22.155 0.096 46.236 0.146 70.317 0.196 94.398 0.246 118.48 0.296 142.56 0.047 22.636 0.097 46.717 0.147 70.798 0.197 94.879 0.247 118.96 13.297 143.04 0.048 23.118 0.098 47.199 0.148 71.280 0.198 95.361 0.248 119.44 0.298 143.52 0.049 23.599 0.099 47.680 0.149 71.761 0.199 95.842 0.249 119.92 0.299 144.00 0.050 24.081 0.100 48.162 0.150 72.243 0.200 96.324 0.250 120.41 0.300 144.49 

1. Kit for the determination of L-carnitine in biological fluids and tissues, consisting essentially of: a) a first container containing Reagent 1, said Reagent 1 being in lyophilized form or in a solution kept at −20° C. and consisting essentially of: HEPES 0.1 M, pH 7.5 EDTA 50 mM, pH 7 acetyl-Coenzyme A DTNB 10.1 mM

b) a second container containing Reagent 2, said Reagent 2 comprising carnitine acetyl transferase.
 2. Kit for the determination of L-carnitine in biological fluids and tissues, consisting essentially of: a) a first container containing Reagent 1, said Reagent 1 being in lyophilized form or in a solution kept at −20° C. and consisting of: HEPES 0.1 M, pH 75 0.652 mL EDTA 50 mM, pH 7 0.174 mL acetyl-Coenzyme A 0.087 mL DTNB 10.1 mM 0.087 mL

b) a second container containing Reagent 2, said Reagent 2 comprising carnitine acetyl transferase.
 3. Kit according to claim 2, in which said first container contains 3 ml of said Reagent
 1. 4. Kit according to claim 1 or 2, in which said container contains 0.500 ml of said Reagent
 2. 5. Kit according to claim 1 or 2, which additionally comprise containers containing L-carnitine standards.
 6. Kit according to claim 1 or 2, in which the reagents of the second container are in lyophilized form.
 7. Method for the determination of total carnitines in a biological tissue or fluid, comprising the steps of: a) subjecting a sample of said biological tissues or fluids to alkaline hydrolysis; and b) determining L-carnitine in said biological tissue or fluid using the kit according to claim
 1. 8. Method according to claim 7, wherein said fluid is selected from the group consisting of plasma, seminal fluid and urine.
 9. Method for the determination of total carnitines in a biological tissue or fluid, comprising the steps of: a) subjecting a sample of said biological tissues or fluids to alkaline hydrolysis; and b) determining L-carnitine in said biological tissue or fluid using the kit according to claim
 2. 10. Method according to claim 9, wherein said fluid is selected from the group consisting of plasma, seminal fluid and urine. 